Replacement heart valves or heart valve prostheses have been fabricated or manufactured for the last forty years. Such devices have been assembled from a variety of materials. Specifically the materials have been of biologic or artificial nature, generally leading to two distinct categories of the prostheses as biological or mechanical replacement heart valves.
The prosthetic heart valves are fabricated to replace the natural heart valves that, because of disease, congenital malformations, ageing or trauma have become dysfunctional and require repair to their functional elements or partial or complete replacement. Characteristics for a desirable prosthetic heart valve may include hemodynamic performance, thrombogenicity, durability and ease of surgical implantation.
Human heart valves under the conditions of normal physiological functions are passive devices that open under the pressure of blood flow on their leaflets. There are four valves in the heart that serves to direct the flow of blood through all chambers in a forward direction. In general, blood leaves the heart lower chambers in the direction to the rest of the body or to the lungs for required oxygenation, or blood enters the lower chambers from the upper chambers of the heart. Similarly, they close under the pressure exerted on the same leaflet elements when blood flow is retrograde, thus impeding return of blood flow to the chamber it has just left. This, under normal conditions, (that is, when the body is not under physical stresses and the heart is beating at the normal resting state of about 70 beats per minute) equates to the leaflets opening by separation from each other, thereby producing an opening or closing by apposing to each other approximately 38 million times per year. It can be surmised that under stress conditions this may be happening at higher rates, thus increasing the number of separations and appositions, as well as the forces of impact between the leaflets during the closing.
When disease conditions affect the structure of the materials of the components of the valve apparatus, the valve itself will decay, degenerate or disrupt and require repair or replacement to restore proper function necessary for the continuation of life.
The shape of the leaflet and surrounding elements of a valve or a valve apparatus is dependent on the function of the heart. In the case of the atrioventricular valves, otherwise known as mitral (in the left lower chamber of the heart) and tricuspid (in the right ventricle), the valve is part of a continuum that extends from the myocardium or muscular wall of the lower chambers, through the papillary muscles, to which is attached a confluence of tendinous rope-like elements known as chordae tendinae that themselves are attached to the edges of differently shaped leaflets which form the flow-allowing and flow-stopping or obstructing elements (leaflets). These leaflets continue and end at a ring-like structure usually known as annulus, that is part of the skeleton of the heart. It is this continuum which should be called an apparatus rather than just valve.
Thus, there is a tricuspid valve apparatus in the right ventricular chamber, and more importantly the mitral valve apparatus within the lower left heart chamber or left ventricle, the pumping function of which provides the systemic flow of blood through the aorta, to keep all tissues of the body supplied with oxygenated blood necessary for cellular function and life. Hence during the cardiac cycle, the valves function as part of a unit composed of multiple interrelated parts, including the ventricular and atria walls, the valve leaflets, the fibrous skeleton of the heart at the atrioventricular ring, and the subvalvular apparatus. The subvalvular apparatus includes the papillary muscle within the ventricle, and the chordae tendinae which connect the papillary muscle to the valve leaflets.
Aortic and pulmonary valves have been replaced with simple trileaflet chemically treated biological valves obtained from animals, or bileaflet mechanical valves without extreme deficiencies in valvular or cardiac function. This is not the case when mitral or tricuspid valves are replaced and the necessary involvement of chordae tendinae and muscular element of the chamber wall are not united to function in harmony with the valve leaflets. Those valves used in the aortic position cannot alone replace the mitral valve apparatus without anatomical and functional compromise.
Aortic stenosis is a disease of the aortic valve in the left ventricle of the heart. This aortic valvular orifice can become tightly stenosed, and therefore the blood cannot anymore be freely ejected from the left ventricle. In fact, only a reduced amount of blood can be ejected by the left ventricle which has to markedly increase the ventricular chamber pressure to pass the stenosed aortic orifice. In such aortic diseases, the patients can have syncope, chest pain, and mainly difficulty in breathing. The evolution of such a disease is disastrous when symptoms of cardiac failure appear and many patients die in the year following the first symptoms of the disease.
The only commonly available treatment is the replacement of the stenosed aortic valve by a prosthetic valve via open-heart surgery. If surgery is impossible to perform, i.e., if the patient is deemed inoperable or operable only at a too high surgical risk, an alternative possibility is to dilate the valve with a balloon catheter to enlarge the aortic orifice. Unfortunately, the result is sub-optimal with a high restenosis rate.
Aortic stenosis is a very common disease in people above seventy years old and occurs more and more frequently as the subject gets older. Until recently, the implantation of a valve prosthesis for the treatment of aortic stenosis is considered unrealistic to perform since it is deemed difficult to superpose another implantable valve on the distorted stenosed native valve without excising the latter.
Percutaneous Catheter-Based Delivery
Andersen et al. in U.S. Pat. No. 6,168,614, entire contents of which are incorporated herein by reference, discloses a heart valve prosthesis for implantation in the body by use of a catheter. The valve prosthesis is consisted of a support structure with a tissue valve connected to it, wherein the support structure is delivered in a collapsed shape through a blood vessel and secured to a desired valve location with the support structure in the expanded shape. However, the support structure is a generally fixed expandable-collapsible structure with little flexibility of modifying configuration at the collapsed shape for easy delivery percutaneously.
Andersen et al. in U.S. Pat. No. 5,840,081 and U.S. Pat. No. 5,411,552, entire contents of both of which are incorporated herein by reference, discloses a system for implanting a valve in a body channel comprising a radially collapsible and expandable stent with a valve mounted to it and a catheter for introducing and securing the valve in the body channel. The catheter generally comprises an expandable member about which the cylindrical stent may be positioned together with the valve, fastening means on the expandable member on which the stent may be mounted to the expandable member, and a channel extending through the catheter for injecting a fluid into the expandable member so as to expand the expandable member from a collapsed profile suitable for introduction into the body channel to an expanded profile in which the stent engages the inner wall of the body channel so as to secure the valve therein. Again, the cylindrical stent is a generally fixed expandable-collapsible structure with little flexibility of modifying configuration at the collapsed stage for easy delivery percutaneously. This type of design is inherently fragile, and such structures are not strong enough to be used in the case of aortic stenosis because of the strong recoil that will distort this weak structure and because they would not be able to resist the balloon inflation performed to position the implantable valve.
Letac et al. in U.S. Patent Application Ser. No. 2001/0007956 and No. 2001/0010017, entire contents of both are incorporated herein by reference, discloses a valve prosthesis for implantation in a body channel comprising a collapsible valvular structure and an expandable frame on which the valvular structure is mounted. However, the expandable frame is a generally fixed expandable-collapsible structure with little flexibility of modifying configuration or minimizing the profile at the collapsed stage for easy delivery percutaneously.
It is one aspect of the present invention to provide a percutaneously deliverable heart valve prosthesis comprising a tissue valve mounted on a support structure that has a plurality of collapsible crossbars with securing rings movably coupled any two adjacent crossbars at an appropriate location upon expanding the support structure of the implantable heart valve prosthesis.
Percutaneous Intercostal Delivery
Various surgical techniques may be used to repair a diseased or damaged valve, including annuloplasty (contracting the valve annulus), quadrangular resection (narrowing the valve leaflets), commissurotomy (cutting the valve commissures to separate the valve leaflets), or decalcification of valve and annulus tissue. Alternatively, the valve may be replaced, by excising the valve leaflets of the natural valve, and securing a replacement valve in the valve position, usually by suturing the replacement valve to the natural valve annulus.
A conventional procedure for approaching the left atrium is by intravascular catheterization from a femoral vein through the cardiac septal which separates the right atrium and the left atrium. In some aspects, this intravascular procedure is not only dangerous and tedious because of long tortuous route, but also limited use because of the catheter size suitable for insertion intravascularly.
Sterman et al. in U.S. Pat. No. 6,283,127, entire contents of which are incorporated herein by reference, discloses a device system and methods facilitating intervention within the heart or great vessels without the need for a median sternotomy or other form of gross thoracotomy, substantially reducing trauma, risk of complication, recovery time, and pain for the patient. Using the device systems and methods of the invention, surgical procedures may be performed through percutaneous penetrations within intercostal spaces of the patient's rib cage, without cutting, removing, or significantly displacing any of the patient's ribs or sternum. The device systems and methods are particularly well adapted for heart valve repair and replacement, facilitating visualization within the patient's thoracic cavity, repair or removal of the patient's natural valve, and, if necessary, attachment of a replacement valve in the natural valve position.
Of particular interest in the present application are techniques for the implantation of an atrioventricular valve that can be retracted or folded inside a delivery system or cannula for delivering through a less invasive intercostal penetration to the desired place, particularly in a left atrium. Thereafter the retracted valve with a support structure is released, expanded, crossbars secured by securing rings, separated from the delivery system, and secured to the desired anatomical place with a minimally invasive technique.
Most tissue valves applicable in the present invention are constructed by sewing the leaflets of pig aortic valves to a stent to hold the leaflets in proper position as a stented porcine valve. They may also be constructed by removing valve leaflets from the pericardial sac of cows or horses and sewing them to a stent as a stented pericardium valve. The stents may be rigid or slightly flexible and covered with cloth (usually a synthetic material sold under the trademark Dacron™ or Teflon™) and attached to a sewing ring for fixation to the patient's native tissue. In one embodiment, the porcine, bovine or equine tissue is chemically treated to alleviate any antigenicity.
The main advantage of tissue valves is that they do not cause blood clots to form as readily as do the mechanical valves, and therefore, the tissue valves do not typically require life-long systemic anticoagulation. Another advantage is that a tissue valve is so flexible that it can be shaped and configured for delivery percutaneously. However, the presence of the support structure consisted of a stent and sewing ring prevents the tissue valve from being anatomically accurate in comparison to a normal heart valve. It is one aspect of the present invention to provide a prosthetic heart valve with the expandable-collapsible support structure having flexibility of modifying configuration at the collapsed stage for easy delivery percutaneously.
Therefore, it would be desirable to provide a delivery system for delivering a prosthetic heart valve to a patient's heart configured to be releasably folded inside a lumen of the delivery system through a percutaneous intercostal penetration of a patient's chest or an opening at a carotid artery, jugular vein, subclavian vein, femoral vein and other blood vessel.